Do I need T3 if I'm going to paint it?

Next question: I noticed 2024 comes in T3 and bare. This is a white argosy, and I'll be patching interior and exterior with what I buy. Do I need the t3 coating (or is it just a finish ?) also should I go .032 or .040



Money isn't a huge issue, I just want to do it right. What is the original metal?



Thanks!